A separator original sheet used for a lithium-ion battery is slit (cut) in a lengthwise direction of the original sheet, and it is thus possible to obtain a plurality of long separator sheets each of which has a predetermined slit width in a direction perpendicular to the lengthwise direction.
Each of the plurality of long separator sheets is wound on a core and is then supplied to a battery production process as a separator roll. In the battery production process, each of the plurality of long separator sheets is cut in a predetermined length in a direction perpendicular to the slit width, and is thus used as a separator.
As such, a lateral surface itself of the long separator sheet which has been obtained by slitting serves as a lateral surface of a battery separator, and therefore a shape of the lateral surface is important.
In view of this, Patent Literature 1 discloses a separator which includes a base material layer and an inorganic layer and has a lateral surface that is formed into a taper shape in order to inhibit the inorganic layer from being peeled off from the base material layer in a case where the separator is bent.
Meanwhile, Patent Literature 2 discloses that a photosensitive material is cut with a shear cutting method so that a lateral surface thereof lies at a right angle.